Bootstrap Current
A self-generated toroidal electric current in a tokamak plasma driven by trapped particle banana orbits in steep pressure gradients.
Governing formula
I_bootstrap ∝ √ε (k_B / B_poloidal) (dn / dr)
SI unit
MA (Plasma Current Fraction)
In depth
In toroidal geometry, trapped particles follow banana-shaped orbits. Radial density gradients create an asymmetric momentum transfer between trapped and passing particles, driving a self-sustaining toroidal bootstrap current that reduces required external transformer drive.
Examples in the real world
Advanced tokamak reactor designs operating with >80% non-inductive bootstrap current fraction.